View Full Version : jetting help!

03-16-2003, 08:14 AM
i have an rs 250 1998
i am putting full arrow exhaust, AF1 Racing High-performance Air Filter and change the main jet to 300/310.

my bike work better than stock 270/280.
it worths trying other jetting?
Arrow recomend 260/270 but this jetting i have trying it.


03-16-2003, 03:13 PM
Arrows recommend going down one size. AF1 high flow filter recommend going up one size. Result with that combo leave main jets as standard.

I'm planning the same combo of exhaust and filter.

So what do the experts think.

Will it work.

03-16-2003, 04:13 PM
All engines work slightly differently so the best thing to do is get it along to a dyno before going mad on it. My RS works fine with Arrow's on a size smaller jet but the dyno operator said it would be unsutable for very cold weather (not that I'd ever use it in the cold so it's ok).

03-16-2003, 05:52 PM
i dont know what must be do!

Stu Jones
03-17-2003, 01:18 AM
All bikes run differently so you must set up your bike with the jetting it needs, either on a dyno or by doing plug chops. Plug chops are when you run the bike in a high gear then pull in the clutch and hit the kill switch at the same time, you then stop remove the plugs and check the clolour of them.

03-18-2003, 07:15 PM
People in the US (including me) with aftermarket pipes typically run either a 260/270 main jet combo, or as Monson suggested, a 250/260 combo. I have yet to find a setup suggested by anyone successful at racing these bikes where the main jets need to be larger than stock! I raced my bike in MIchigan in temps from the thirties (F) to over 100 (F) on the stock jetting without problems. Only now that I have switched to the 316 kit have I needed to jet down (that's right! 12 more HP, but smaller main jets...go figure) to make it work. The modified engine is more sensitive to jetting changes than the stocker.

colin skiliicorn
03-19-2003, 04:32 AM
The reason you are using smaller jets with your big bore conversion is because as with any two stroke engine if it is making more power it wants to suck more fuel & air into it so it is sucking harder but getting more fuel through a smaller jet. If you want ot clarify this log on to the TZ 250 web site & go into links & there is a section there on jetting & it explains jetting in great detail

03-19-2003, 12:16 PM
I'm always interested in reading about tuning @ jetting.. which TZ 250 site are you referring to? URL?

03-19-2003, 12:21 PM
Nevemind.. I'm supposing you're talking about this...
users.oc-net.com/dgriffit...tting.html (http://users.oc-net.com/dgriffiths/twostrokejetting.html)

04-21-2003, 04:58 PM
why smaller jetting?
is better?

If i am jetting with bigger will have a problem?